An example of the conventional power train of the above-noted type is known e.g. from the Japanese Unexamined Patent Application Publication No. 2003-130177. This power train includes a hydrostatic stepless speed changer mechanism and a planetary gear mechanism and configured such that a pump side input gear is fixedly mounted on a pump output shaft extending through a rotational axis of a hydraulic pump of the hydrostatic stepless speed changer mechanism, and as this pump side input gear meshes a gear formed in a carrier, the engine power is inputted to the planetary gear mechanism. With this type of power train for a tractor, engine power not subject to the speed changing effect by the hydrostatic stepless speed changer mechanism is inputted to a predetermined rotary body that constitutes the planetary gear mechanism. However, a problem as follows would tend to occur.
Namely, the hydrostatic stepless speed changer mechanism is to be assembled in such a manner that the pump and the motor of this hydrostatic stepless speed changer mechanism are juxtaposed to each other along the transverse direction of the vehicle body on the front side of the vehicle body as seen in a plan view of the vehicle body. In this, with the conventional power train of this type, transmission means for inputting the engine power not subject to the speed changing effect by the hydrostatic stepless speed changer mechanism to the planetary gear mechanism is interposed between the hydrostatic stepless speed changer mechanism and the planetary gear mechanism, so there arises a need to assemble the hydrostatic stepless speed changer mechanism and the planetary gear mechanism in a spaced relationship from each other in the fore/aft direction of the vehicle body.